Nunn’s Applied Respiratory Physiology Eighth Edition 8e eBook PDF Download
Breathing is normally possible through either the nose or the mouth, the two alternative air passages converging in the oropharynx. Nasal breathing is the norm and has two major advantages over mouth breathing: filtration of particulate matter by the vibrissae hairs and better humidification of inspired gas.
Humidification by the nose is highly efficient because the nasal septum and turbinates greatly increase the surface area of mucosa available for evaporation and produce turbulent flow, increasing contact between the mucosa and air. However, the nose may offer more resistance to airflow than the mouth, particularly when obstructed by polyps, adenoids or congestion of the nasal mucosa.
Nunn’s Applied Respiratory Physiology Eighth Edition
Phonation, the laryngeal component of speech, requires a combination of changes in position, tension and mass of the vocal folds (cords).
Rotation of the arytenoid cartilages by the posterior cricoarytenoid muscles opens the vocal folds, while contraction of the lateral cricoarytenoid and oblique arytenoid muscles opposes this. With the vocal folds almost closed, the respiratory muscles generate a positive pressure of 5 to 35 cmH2O which may then be released by slight opening of the vocal folds to produce sound waves.
The cricothyroid muscle tilts the cricoid and arytenoid cartilages backwards and also moves them posteriorly in relation to the thyroid cartilage. This produces up to 50% elongation and therefore tensioning of the vocal folds, an action opposed by the thyroarytenoid muscles, which draw the arytenoid cartilages forwards towards the thyroid shortening and relaxing the vocal folds. Tensioning of the folds results in both transverse and longitudinal resonance of the vocal fold allowing the formation of complex sound waves.